1. Field of Invention
The present invention relates to an optical detection method and an optical Micro-Electro-Mechanical System (MEMS) detector; particularly, it relates to a MEMS device in which capacitance detection is replaced by optical detection. Such MEMS device can be employed to form, for example, an accelerometer. The present invention also relates to a method for making the optical MEMS detector.
2. Description of Related Art
Present MEMS accelerometers detect displacement usually by measuring capacitance variations. As shown in FIG. 1, a capacitance-type accelerometer typically includes a fixed electrode 1 and a movable electrode 2; when the movable electrode 2 is moved, the capacitance-type accelerometer detects the capacitance variation between the electrodes 1 and 2 to determine acceleration. The structure shown in FIG. 1 can be either a top view (detecting the capacitance variation in horizontal direction) or a cross-section view (detecting the capacitance variation in vertical direction).
U.S. Pat. No. 6,763,718 discloses another type of prior art: an optical-type accelerometer as shown in FIG. 2, wherein light is reflected back and forth between two mirrors 3 and 4 to create a Fabry-Perot resonance such that only light with specific wavelengths can get to a photo diode 5. However, the structure of this optical accelerometer is very complicated. In order to achieve the Fabry-Perot resonance, the distance between the two mirrors 3 and 4 needs to be very precise; to this end, this prior art needs to provide an adjustment mechanism. Furthermore, two mirrors 3 and 4 need to be form respectively on the surfaces of the membrane 6 and the substrate 7, and the mirrors must be capable of causing partial transmission and partial reflection. Hence, the foregoing optical accelerometer requires a very complicated fabrication process, with high cost.
In view of the above, the present invention provides an optical MEMS detector to solve the foregoing problems in the prior art.